I would like more to see curated hand picked math problems instead of mass imported problems from various sources. Along with solutions and detailed explanations and links to the theory needed to understand and solve the problem.
Handpicking best problem and writing detailed explanations could be quite hard for one person, but if a lot of people find someones explanation useful and insightful, and vote for it, then one person could handpick from roster of problems with good explanations.
That would also help platform by engaging visitors to not only learn math, but to teach the parts they know well to others. (I also found out that explaining math to others really helps you to understand it better, so win|win)
> Suppose that one digit, indicated with a question mark, in each of the following ISBN-10 codes has been smudged and cannot be read. What should this missing digit be?